1. Field of the Invention
The present invention relates to a system to electronically control the temperature of a plant.
2. Description of the Related Art
WO 2002/070873 describes a device and method for diagnosing internal combustion engines and a control method of the internal combustion engines with the diagnosis device and method, while Japanese Patent Application Publication No. 2006-183645 describes a system for controlling the temperature of a plant that is a controlled object.
The technology in WO 2002/070873 features detection of catalyst degradation by defining a model used to estimate the temperature of a catalyst and comparing the output from the model and the output from a temperature sensor installed in the catalyst. When the temperature sensor output indicates a temperature equal to or lower than the light-off temperature of the catalyst, the system corrects the estimated temperature obtained from the model based on the temperature sensor output.
The technology in Japanese Patent Application Publication No. 2006-183645 features control of the temperature of a catalyst to be a predetermined target value by defining a model used to estimate the catalyst temperature and changing engine operating parameters (ignition timing and target air/fuel ratio) based on the output from the model. In the control operation, the system compares the output from the model and the output from a temperature sensor installed in the catalyst to provide a deviation therebetween on which the correction of the model's coefficient is based.
In recent years, demand for rapid warm-up of exhaust system down-stream-treatment devices (catalyst, lean NOx catalyst, selective catalytic reduction (SCR) system, etc.) of gasoline engines and diesel engines has been growing for the purpose of reducing emissions immediately after start-up of the engine. In order to minimize fuel efficiency degradation and the emissions produced before activation of the down-stream-treatment devices, monitoring the temperature of the down-stream-treatment devices and controlling control parameters (ignition timing, fuel injection amount, fuel injection pattern, etc.) of the engine are also needed so as to have an optimal temperature-rise pattern. Additionally, lean-burn gasoline engines, auto-ignition combustion engines, variable lift engines, diesel engines and some other engines discharge exhaust gas at low temperatures even after the warm-up of the engines and may not activate their down-stream-treatment devices depending on their operating conditions. There is another demand for control of the temperature of the down-stream-treatment devices for the reason that the temperature range in which the down-stream-treatment devices can satisfactorily work is limited. A possible solution to meet the demands is to install a temperature sensor on the down-stream-treatment device and to control the control parameters ignition timing, fuel injection amount, fuel injection pattern, etc.) of the engine based on the output from the temperature sensor. However, the temperature sensor installable on the exhaust system are made to deal with environmental conditions, including temperature difference, corrosive elements (water, sulfuric acid, etc.) and vibration, to which the temperature sensor is exposed, and therefore cannot allow its responsivity to reach a level at which the above-described requirements to control the temperature are fully satisfied. To solve the problem, the system in Japanese Patent Application Publication No. 2006-183645 sets a model for estimating the temperature of the down-stream-treatment device, controls the control parameters of the engine based on the output from the model, and corrects the “coefficient (constant Dcat)” of the model based on the deviation between the model output and the temperature sensor output so as to prevent the output value of the model from differing from the output value of the sensor at a steady state.
However, Japanese Patent Application Publication No. 2006-183645 employing a sequential least square method that can correct only the coefficient (constant) of linear models cannot correct nonlinear functions (table and map).
Down-stream-treatment devices often change its exothermic properties into nonlinear exothermic properties according to the temperature. In a case where the temperature of the down-stream-treatment device needs to be increased or decreased in a short period of time (e.g., post-startup rapid warm-up control and regeneration control of diesel's DPF (Diesel Particulate Filter), etc.), the technique in Japanese Patent Application Publication No. 2006-183645 cannot provide adequately accurate model outputs, which may cause an increase of emissions, fuel efficiency degradation and acceleration of down-stream-treatment-device degradation due to excessive rise of temperature. In addition, the technique in WO 2002/070873 achieves only correction of the model's coefficient/constant, and limits the correction timing to a time before the activation of the down-stream-treatment device.